The present invention generally relates to electrical power supplies, and particularly relates to output voltage positioning control.
Electronic devices of all types are an integral part of everyday life. While the purposes served by these devices is widely varied, from cell phones to GPS receivers, to portable or desktop computers, the devices themselves have several characteristics in common. For example, with the increasing sophistication of the average consumer and the competitive market pressure attendant with that sophistication, the capabilities and features of modern electronics advances at a relentless pace. Advances in device capability or speed generally arise from building in more powerful computational systems at the core of these electronic devices.
At the heart of these computational cores are advanced microprocessors or other digital logic devices. In tracing the pace of development for digital electronics, one sees an almost stunning rate of increase in device complexity and sophistication. Modern microprocessors, as well as other types of advanced devices like field programmable gate arrays (FPGAs) and application specific integrated circuits (ASICs), may include tens of millions of transistor devices and operate at clock speeds well over 1 GHz. Both electrical and economic constraints limit the size of high-performance integrated circuits, and so chip designers continually shrink the basic geometries of the semiconductor devices or elements comprising these large integrated circuits.
With shrinking geometries come advantages in physical packaging and lower operating voltages. The lower operating voltages permit higher clock speeds because of reduced signal swing and substantial savings in operating power. For example, a few short years ago, digital logic, including many microprocessors, commonly operated at 5 VDC, while it is not uncommon today for advanced microprocessors to operate at 1.25 VDC or lower. Even at these greatly reduced operating voltages, these modern digital circuits require significant operating current. Indeed, maximum current draw for high-end microprocessors may be in excess of fifty amps. Moreover, the instantaneous current requirement for such devices may change suddenly, such as when going from an idle state to a full active condition.
Powering these types of electronic loads is a multi-faceted challenge. Typically, such electronics have tight operating voltage specifications, meaning that the supply voltage provided to them is allowed to vary only slightly across the full range of device operating conditions. Meeting these tight supply voltage limits is exacerbated by the large dynamic range of required load current, and particularly by the rapid rate of change of required load current.
An apparatus and method provide bounded voltage droop, which facilitates active voltage positioning in power supply applications. A bounded droop circuit generates a droop voltage based on load current, such that the output voltage provided to the load by an associated power supply drops below its nominal value by an amount determined by the droop voltage. The droop circuit includes a droop limiter that establishes a maximum droop voltage that is independent of load current, thereby preventing the output voltage from dropping below a minimum operating voltage of the load.
Because the droop limiting function establishes an accurate maximum droop voltage, the bounding limit may be set substantially at the lower operating limit of the load, thereby allowing the power supply to take full advantage of the load""s operating voltage range. Drooping to the minimum operating voltage can save operating power and minimizes any voltage overshoot at the load arising from sudden reductions in load current.
The bounded droop circuit may be implemented such that it provides a discrete droop voltage, or provides a droop voltage that is linearly proportional to the load current up to the bounding point. In either case, the bounding point establishes the maximum droop voltage and corresponding minimum output voltage. The bounded droop circuit may be incorporated into a power supply controller, such as a switch-mode controller. If integrated into a larger power supply controller, the operating limits, such as the maximum allowable droop voltage, may be set via external components. This allows significant flexibility from the perspective of system designers.